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The “Georeactor” Hypothesis.

This post was inspired, in part at least, by Rod Adams’ post on NEI Nuclear Notes recently, asking about the georeactor theory. I hope you find it useful, Rod.

The “georeactor” hypothesis is a proposal by J. Marvin Herndon that a fissioning critical mass of uranium may exist at the Earth’s core and indeed that it serves as the energy source for the Earth’s magnetic field. You can read all about Herndon’s ideas at his website.

Herndon’s georeactor hypothesis is not widely accepted at all by the scientific community, outside of Herndon himself and a very small number of defenders.

Herndon’s georeactor hypothesis is sometimes confused with the existence of natural nuclear fission reactors in the Earth’s crust in rich uranium deposits at Oklo in Western Africa – however, it must be stressed that these are not the same thing – there is absolutely no doubt at all, scientifically, as to the occurrence of nuclear fission and the formation of natural nuclear “reactors” at Oklo approximately two billion years ago.

However, Rob de Meijer and associates at the Nuclear Physics Institute in Groningen, the Netherlands, are amicable towards Herndon’s theory, and have indeed proposed an experiment by which it should be somewhat falsifiable – involving measurement of the antineutrino flux from the Earth’s core which they believe will validate the georeactor hypothesis.

Fission reactors generate huge numbers of electron antineutrinos – about 10^26 per day from a typical manmade power reactor. Several thousand of these can be measured per day in a detector of modest size, outside the reactor, outside the containment, tens of meters away.

The antineutrinos resulting from each fission event from uranium and plutonium have different total count rates and energy spectra – the antineutrinos are not actually produced by nuclear fission itself, but rather by the beta decay of fission products. The antineutrinos therefore carry with them information about the amount and type of fissile material in the reactor core, and the rate at which it is being fissioned.

Because of this, incidentally, the use of neutrino detectors has raised considerable interest in recent times in the context of providing a real-time online and very simple measurement of the fuel burnup, operating status, power level, plutonium production and such characteristics of operating nuclear reactors, which is of considerable utility in enforcing non-proliferation safeguards.

(There’s more information on this application here if you’re interested.)

Personally, I don’t see why existing underground neutrino observatories, such as Super-Kamiokonde, the Sudbury Neutrino Observatory, and the IceCube experiment in Antarctica shouldn’t be sufficient to provide significant insights into the presence – or absence – of georeactor antineutrinos. Clearly all neutrinos from a “georeactor” come exclusively from exactly the centre of the earth as observed at every detector, and they should be detectable at all neutrino observatories worldwide with a similar flux everywhere.

Combining these simple pieces of information with the expected energy spectra of neutrinos from uranium fission, it seems extremely plausible that the georeactor hypothesis can well and truly be put to the test, using existing experiments, and probably even with existing collections of raw data from these experiments.

Uranium, being incompatible in an iron-based alloy, is expected to precipitate at a high temperature, perhaps as the compound US. As density at Earth-core pressures is a function almost exclusively of atomic number and atomic mass, uranium, or a compound thereof, would be the core’s most dense precipitate and would tend to settle, either directly or through a series of steps, by gravity to the center of the Earth, where it would quickly form a critical mass and become capable of self-sustained nuclear fission chain reactions.

Of course, there is what seems like one significant problem with this theory – whilst several billion years ago, the portion of uranium-235 in natural uranium was much higher than it is today – equivalent to that of manmade enriched uranium, because U-235 decays faster than U-238, although a much larger ratio of U-235 was originally formed when the uranium was formed inside supernovae than is seen in the Earth today. That is why fission occurred at Oklo two billion years ago, but does not occur today – there is not enough of a concentration of U-235 in nature. Therefore, how can a “georeactor” exist?

Herndon explains away this question by postulating that the georeactor is something like a fast breeder reactor, started up aeons ago when the U-235 was more abundant, and today burning the abundant U-238 into plutonium-239.

However, if this is the case, couldn’t it be likely that we could observe plutonium-fissioning “breeder reactors” in rich uranium deposits in the Earth’s crust, like at Oklo, today?

4 Responses

Personally, I don’t see why existing underground neutrino observatories, such as Super-Kamiokonde, the Sudbury Neutrino Observatory, and the IceCube experiment in Antarctica shouldn’t be sufficient to provide significant insights into the presence – or absence – of georeactor antineutrinos.

I think some of the observatories would only detect neutrinos made by proton to neutron conversion & not the anti-neutrinos produced by neutron to proton conversion.

However, IINM the SNO can detect by several different interactions some of which would work on anti-neutrinos.

Thank you for the thoughtful commentary – even though it contains several additional questions instead of answers.

One possible answer to your final thought – the concentration of heavy metals in the core could be quite different from those existing in the crust, mixed in with other minerals and substances like water. The Oklo reactors are pretty well established to have been thermal reactors with a moderator – water – that does not lead to effective breeding ratios. There, the fuel – U-235 – was consumed without producing enough new fuel from U-238 to keep the reactor going. I think that Herdon’s thought is at least plausible that a fissioning core could keep itself going through the use of a near 1.0 conversion ratio, especially since it would have initiated when the U-235 concentration was much higher.

Experimentation as you suggest would certainly do much to improve our understanding, and I think that Dr. Herndon has suggested similar experiments. I am not a scientist and not really all that interested in spending gobs of money to support or discredit a theory. It seems that if neutrinos are as detectable as you say, that it might be possible to do the experiment without too much cost.

Hi
i have to admit that i didnt yet read all of your post. However, I have to add some piece of information on recent neutrino detectors. From the Borexino experiment a upper limit for the energy output of such a georeactor could be deduced. It is around 3TW. Thus the theory of the georeactor can not be ruled out. There is a new experiment proposed that will hopefully be able to improve the limit further (http://www.e15.ph.tum.de/research_and_projects/lena/).